I test drove a couple GTS and they are great cars. check out the viper forum i think its viperalley.com, google it. They are very helpful over there in pointing out what to look for in a used GTS. As someone else said that car on ebay is BS. I think only around 100 GTS-R's were made, and were only available in 1998. They will cost over 100k due to the rarity.
example:
Viper GTSR
But overall get a 98+ GTS and check out the viper forum to get questions answered more thoroughly